LEPUS CUNICULUS 269 



portal system is present as in all Craniates, but a renal portal system 

 is absent. The mammals are warm blooded, that is to say, the blood 

 is maintained at a fairly constant temperature somewhere just 

 below 100 Fahr., and this is quite independent of the variations 

 of the temperature of the surroundings. 



The brain is extremely well developed in the mammals, 

 particularly in the cerebral hemisphere which in some animals, 

 for example man, forms the largest part of the brain. Their surfaces 

 are thrown into a series of folds or gyri, separated from one another 

 by well-defined grooves or sulci, whereby the amount of space at 

 the periphery of the hemispheres, in which the nerve cells lie, is 

 greatly increased. The main part of this increase is due to the 

 formation of a new portion of the roof of the cerebrum termed the 

 neo-pallium, which is not found in the lower animals. The optic 

 lobe on each side is divided so that there are two pairs of bodies, 

 the corpora quadrigemina. The sense organs are also strongly 

 developed, and in the internal ear we find a spirally coiled structure, 

 the cochlea. 



With this short discussion of the general characters of the class, 

 we can pass on to consider a particular example in the rabbit. 

 Lepus cuniculus, the ordinary wild rabbit, belongs to the genus 

 Lepus, which includes among other forms L. timidus the hare, and 

 L. variabilis, the Arctic hare or Snowshoe rabbit. It is a very common 

 animal in practically all parts of the British Isles, and is the species 

 most widely kept in captivity when, as is well known, it exhibits a 

 wide range of variation in colour, general size and build, and so on. 

 This phenomenon of variation under domestication is a common one, 

 and is marked in cats, dogs, cattle, pigeons, fowls, etc., to a greater 

 or less extent when they are domesticated by man. Years ago the 

 rabbit was introduced into Australia, where, free from the enemies 

 and other checks that keep its numbers down in its native lands, it 

 has multiplied to such an extent that it has become a serious menace 

 to the farmers. This is an illustration of what may happen when the 

 equilibrium in the animal life of a given area that is established in 

 the course of a long period of time, is upset by man introducing a 

 new animal. 



External Features. 



Externally we can readily distinguish in the body of the 

 rabbit a head, a neck, a trunk, a tail and two pairs of limbs, all of 

 which are covered with a dense growth of fine hair, the fur. The 

 manus possesses five digits, while the pes has only four. The colour 

 in the wild form is a dark brownish-grey above, shading off to a 

 lighter grey on the sides, and becoming practically white underneath. 



